In this known switch a contact terminal common to both switch conditions in a holder, an elastically deformable contactor, an actuating element, a first and a second selective terminal, and a lever are arranged in a housing. The elastically deformable contactor comprises an essentially elongated tension strip and an arched area which, seen from above, is arranged parallel to the tension strip. The contactor also comprises an area that connects the tension strip and the arched area, which has a contact point arranged on each side of the arch. By means of an actuator which can be operated from outside, the elastic contactor is deformed elastically from a normal position in which it is in contact with to a first selective terminal, in such manner that the contactor is brought into contact with a second selective terminal. When the actuator is released, the elastically deformable contactor is relaxed, at least partially, and returns to its normal position, so that the actuator too returns to its initial position.
Switches of this type are inter alia made in the miniature or sub-miniature range and fulfill switching tasks in which a normally closed electric contact is temporarily interrupted by mechanical action upon the actuator or a connection to a second contact is made, which is maintained for as long as the actuator is in the switching position. In other applications, however, the actuator or the contactor can be fixed in place.
Switches of this type are particularly suitable for position-detection purposes in automatic processes. Typical fields of application, however, can also be closing systems, vehicle body and inside areas, and various position tests in household appliances or other mechanisms.
DE 1 989 468 indicates to those familiar with the field that relative movement between the contact points which is substantially perpendicular to the switching direction is advantageous, because the contact points remain free from wear or dirt particles. The relative movement in the switch is produced by longitudinal extension of a central spring/switching spring divided into two zones. In this case a rigid zone of the switching spring is moved through an angle, which for its part is deflected by an actuating spring, in the longitudinal direction of the switch. During this extension of the switching spring the lower, meander-shaped part of the switching spring is deformed elastically. This happens because the actuating spring is deflected about the common attachment point with the switching spring in the housing, whereby the switching spring is restricted in its freedom of movement by the two contacts. Consequently, during a deflection movement of the actuating spring beyond the abutment point of the switching spring, relative movement between the actuating spring and the switching spring takes place in the longitudinal direction of the actuating spring, in such manner that the contact point on the touch-zone is moved parallel to the respective contact plane. This elaborate mechanism not only has the disadvantage that three components are needed in order to produce relative movement between the contacts, but the added disadvantage that for the linear movement of the switching spring to be produced, a large rotational deflection of the actuating spring is needed, which in turn leads to a switch of large structure.
The explanatory document DE 1 168 993 also concerns an electric snap-action switch whose purpose is to design the frictional and rolling movements of the contact elements more robustly. In this case a rigid contact arm which is hinge-mounted at its end remote from the contact points is moved one way or the other between two contact terminals by a switching arm. For its part, the switching arm is deflected at one end by an actuating element. The other end of the switching arm is hinge-mounted on a common terminal. To provide support against a first contact in the normal position of the switch there is a C-shaped spring, which when the actuating element is operated, becomes more tightly curved. As a whole the articulated holding of the rigid contact arm and the circular deflection of the switching arm result in an only very small linear movement of the contact point of the rigid contact arm on the contact point of the terminal. Here too, no linear movement of the contact point of the contact arm on the contact surface of the terminal takes place.
DE 1 917 411 U, which is the point of departure of the most closely related prior art, describes an electric switch with a one-piece, elastically deformable contactor configured in three zones: a leaf-spring zone which is flat in any switch condition, a compression spring blade zone, and a free end zone. A first and a second contact point are arranged on the opposite faces of the leaf-spring/switching spring zone. From the switching spring zone there extends a compression spring blade, which rests against a knife-edge support. The free end zone is bent over by about 180° relative to the switching spring and rests against a projection on the housing. When the switch is changed from a normal position, in which the switching spring is touching an upper contact, to a switched position in which the switching spring is touching a lower contact, the curvature of the compression spring blade increases while at the same time the leaf-spring zone (without undergoing any deformation) is moved by the actuating element in the direction of the switch-over point. When the switch-over point has been passed, the switching spring snaps over from the upper contact to the lower contact.
Due to the curvature change of the compression spring blade, until the switch-over point has been reached a slight frictional movement on the connection element (contact) takes place between the switching spring and the contact point of the upper connection element. It has been found that the smaller the structure of the switch, and the shorter that the switching path of the switch is chosen, the smaller is the frictional movement of the switching spring on the respective contact elements.
In the switch known from the prior art as described in EP 0 837 483 A2, a spring mechanism for the contactor is known, which is responsible for switching from a first contact point to a second contact point. In this, in particular the distance between the two selective terminals and the spring strength of the leaf spring are important influencing parameters. Thus, for the known switch it is advantageous to use a relatively strong leaf spring in the arched section, in order to ensure secure contact forces on the first and second contact points. By using so strong a leaf spring the actuation forces for such a spring are also necessarily increased and the tension strip must accordingly be made with the highest possible bend rigidity.
The result of supporting the curved zone with its free end against the common contact terminal is that the contactor is pushed upward, so that contact against the first contact point produces a torque such that the free end of the tension strip, which is attached to the lever, pushes the lever together with the actuating element to the initial position. When the actuating element is moved into the housing, the free end of the tension strip moves over the support point of the arched section, and when this is reached an equilibrium is established such that further movement of the free end of the tension strip triggers linear movement of the end area of the contactor from the first contact point to the second contact point. However, before the contactor moves clear of the first contact point, i.e. before the tension strip reaches the support point of the arched section, linear movement takes place on the first contact point in the longitudinal direction of the tension strip. This happens because the tension strip on the lever, which is attached to and can pivot in the housing, undergoes a circular-arc movement about the pivot point of the lever. At the same time the end area of the contactor is impeded in its movement toward the contact surface by the touch-point of the contact point and therefore completes only that part of the tension strip's movement which is directed in the longitudinal direction of the switch.
Once the switch-over point has been passed, i.e. when the tension strip has moved past the support point of the arched section, the end area changes over from the first contact point to the second contact point. This happens by virtue of an approximately linear movement directed perpendicularly to the tension strip and by a substantially parallel displacement of the contactor in the actuating direction of the actuating element. After the switch-over, as the tension strip moves farther the second contact point of the contactor undergoes an additional curved movement whereby the second contact point rolls on its contact area in the same rotation direction as the curved motion of the tension strip. Accordingly, on the second contact point there is a greatly reduced linear movement or a greatly reduced sliding or rubbing of the contact point over the contact surface in the longitudinal direction of the switch. Under certain geometrical conditions the linear movement of the contact points on the contact surfaces tends toward zero.
In order to be able to switch reliably between the two contact positions even with the often required small actuating forces, at both contact points a linear movement should take place in or against the tension direction of the tension strip, i.e. essentially in the longitudinal direction of the holder or the housing. Such a linear movement on the individual contact surfaces keeps them clean and larger loads can be switched with the same contact pressure than when no such linear movement takes place.
For the known electric switch this means that on the first selective terminal a higher load can be connected than on the second one. Thus, with the known switch the second contact point determines the load that can be connected by the electric switch.
Short current and voltage peaks, for example occurring when capacitative or inductive loads are connected, can result in welding together of the contacts. Thanks to the linear frictional movement of the contact surfaces relative to one another, such welds between contacts are immediately broken again during the actuation of the switch. Thus, the shorter the linear rubbing travel the more probable it is that contact welding will occur. In the known switch, at the second contact point, owing to the rotation movement of the contactor the linear rubbing movement changes to a pure rolling of the contact point on the contact surface. Contamination or particles deposit on the contact surfaces over the life of the switch, and lead to welds between the contact points and the contact surfaces.
In the case of more severe contamination or larger particles, such rolling can lead to failure of the switch since such particles cannot be cleared away from the contact surfaces by the rubbing movement of the contact points.